As Fleet Ballistic Missiles (FBMs) have increased in length and diameter to meet greater range and payload requirements, the nose fairing has become blunter for efficient use of the launch-canister volume. The blunt nose has increased drag, resulting in a range penalty. One technique for increasing range is by deploying an aerospike from the nose fairing of the missile. The aerospike creates a region of flow separation over the nose fairing thereby reducing dynamic pressures within this region which results in reduced drag for the missile. However, the aerospike also forms a shock wave at the nose fairing surface that limits its full range-gaining potential.
U.S. Pat. No. 4,549,464 issued to Hawkins et al. proposes one solution for eliminating the shock wave caused by the deployable aerospike while still maintaining the increased payload capacity benefit of a blunt nose missile. This patent document discloses an inflatable aerodynamic shroud which attaches to the blunt nose cone of the missile. In its stowed position within the launch canister, the shroud is folded flush against the forward surface of the blunt nose cone. Once launched, the shroud is inflated into an aerodynamic deployed position by actuation of a solid propellant gas generator.
As compared to a deployable aerospike-equipped missile having a rigid nose fairing, the inflatable aerodynamic shroud of Hawkins et al. allows for an increase in the cylindrical body portion of the missile thereby providing increased fuel and payload capacity and improved range gaining potential for the missile. A blunt nose cone, however, is not optimum for the efficient packaging of payload elements. Also, it would be desirable to utilize the unoccupied space in the launch canister surrounding the blunt nose cone for further increasing the fuel and payload capacity of the missile.
A desirable feature of an inflatable nose fairing is that it exhibit good flexibility in order to provide compact folding capability into a stowed position so that the missile can be lengthened and yet still fit within a launch canister.
The structure must also be air tight to permit reliable and rapid inflation and have a high tensile strength characteristic sufficient to withstand the dynamic pressures of flight when deployed. Further, the structure must be able to withstand the elevated temperatures which are encountered while traveling at transonic and supersonic velocities. Further still, the nose fairing must be able to withstand the effects of erosion caused by debris, sandstorms, iceclouds, etc.
U.S. Pat. No. 4,921,557 issued to Nakamura discloses a method of fabricating a conically shaped fiber-reinforced elastomeric membrane suitable for use as an inflatable nose fairing for a blunt nose cone of a submarine-launched missile. The elastomeric membrane includes three ply layers of silicone rubber impregnated yarns. The yarns of the first and third ply layers are oriented circumferentially, being applied on a conical mandrel using a helical winding apparatus. The second ply is fabricated by hoop winding silicone rubber impregnated yarns on a constant diameter cylinder and then cutting to form gores of fiber-reinforced rubber material. The gores are then applied to the conical mandrel so that the yarns of the second ply are oriented transverse to the yarns of the first (and third) ply(s). The resulting laminate is a balanced ply construction consisting of a longitudinal ply layer sandwiched between two circumferential or hoop wound ply layers.
Generally speaking, for laminate structures, the thicker the laminate, the less flexible the completed structure will become. In view of the balanced ply construction of Nakamura, there is a limitation as to how thick the ply layers can be made to ensure good flexibility for compact folding of the inflatable nose fairing into the stowed position and still satisfy the thermal, strength and erosion resistance requirements for specific applications. Also, the geometry of a balanced ply construction as disclosed in Nakamura will inherently exhibit high bending stiffness in the longitudinal or axial direction of the nose fairing as the longitudinally arranged fibers of the second ply layer, being located at a distance away from a neutral axis of the cross section through the axial direction of the laminate, are in relatively high strain.
Accordingly, there is a definite need in the art for an improved inflatable nose fairing construction and method of fabrication which overcomes the problems of the prior art.